Systems and methods for use with an implantable medical device for discriminating VT and SVT based on ventricular depolarization event timing

ABSTRACT

Techniques are described for discriminating ventricular tachycardia (VT) from supraventricular tachycardia (SVT) using an implantable medical device capable of multi-site ventricular sensing. In one example, ventricular depolarization events are detected within a patient by the implantable device during a tachyarrhythmia, at both a left ventricular sensing site and a right ventricular sensing site. Ventricular event timing differences are then ascertained. The device compares the ventricular event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient, such as event timing differences previously detected within the patient during sinus rhythm or extrapolated from sinus rhythm values. The device then distinguishes VT from SVT based on the comparison of the event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences. Morphological waveform analysis can also be performed, when needed, to further distinguish VT from SVT.

FIELD OF THE INVENTION

The invention generally relates to implantable cardiac stimulation devices, such as pacemakers, implantable cardioverter/defibrillators (ICDs) or cardiac resynchronization therapy defibrillators (CRT-Ds) and, in particular, to techniques for discriminating ventricular tachycardia (VT) from supraventricular tachycardia (SVT) using such devices.

BACKGROUND OF THE INVENTION

A pacemaker is a medical device for implant within a patient that recognizes various arrhythmias such as tachycardia and delivers pacing therapy to the heart in an effort to remedy the arrhythmia. An ICD is a device, also for implant within a patient, which additionally recognizes atrial fibrillation (AF) or ventricular fibrillation (VF) and delivers electrical shocks to terminate the fibrillation. Within pacemakers and ICDs, it is important to distinguish a tachycardia that arises in the ventricles from those that arise elsewhere in the heart. A tachycardia that arises in the ventricles (referred to as VT) is often more serious than a tachycardia arising elsewhere in the heart, since VT can sometimes lead to VF, which is fatal if untreated. Moreover, the type of therapy to be delivered to the heart of the patient depends upon the source of the tachycardia. In particular, it is important to discriminate SVT from VT. SVT is a tachyarrhythmia whose origin is above the ventricles but which is conducted into the ventricles, resulting in unacceptably rapid ventricular rate. The true underlying arrhythmia in these cases may be AF, sinus tachycardia (ST), ectopic atrial tachycardia, atrial reentry tachycardia, atrioventricular (NV) nodal reentry tachycardia, paroxysmal AF or atrial flutter.

Failure to distinguish SVT from VT can result in delivery of inappropriate therapy. Depending upon the capabilities of the implanted device, inappropriate therapy might include delivery of unnecessary anti-tachycardia pacing (ATP) to the ventricles in response to an SVT (that has been misidentified as VT) or delivery of unneeded cardioversion shocks to the atria in response to a VT (that has been misidentified as SVT.) Misidentification of SVT and VT is one of the leading causes of improper device therapy, inclining the delivery of painful and unnecessary cardioversion shocks.

Accordingly, it would be highly desirable to efficiently and reliably distinguish SVT from VT. Waveform morphology comparison may be employed in an attempt to achieve such discrimination. Waveform discrimination techniques are described in, e.g., U.S. Pat. No. 5,273,049 to Steinhaus, et al. entitled, “Detection of Cardiac Arrhythmias using Template Matching by Signature Analysis”; U.S. Pat. No. 5,240,009 to Williams, entitled “Medical Device with Morphology Discrimination”; U.S. Pat. No. 5,779,645 to Olson, et al., “System and Method for Waveform Morphology Comparison”; and U.S. Pat. No. 6,516,219 to Street, entitled “Arrhythmia Forecasting based on Morphology Changes in Intracardiac Electrograms.” See, also, the improved morphology-based discrimination techniques described in U.S. patent application Ser. No. 11/674,974, filed Feb. 14, 2007, of Graumann, entitled “System and Method for Morphology-Based Arrhythmia Discrimination using Left Ventricular Signals sensed by an Implantable Medical Device.”

Other techniques for distinguishing VT and SVT include “sudden onset discrimination” and “PR logic discrimination.” Sudden onset discrimination is discussed, e.g., in U.S. Pat. No. 6,636,764 to Fain, et al., entitled “Safety Backup in Arrhythmia Discrimination Algorithm.” PR logic discrimination is discussed, e.g., in U.S. Pat. No. 7,058,450 to Struble, et al., entitled “Organizing Data according to Cardiac Rhythm Type.”

However, waveform discrimination, sudden onset discrimination and PR logic discrimination may not be optimal or sufficient in distinguishing VT from SVT, and inappropriate cardioversion shocks continue to be a problem. Also, accurate waveform discrimination can be computationally intensive, thereby consuming device resources.

Accordingly, it would be desirable to provide improved techniques for distinguishing VT and SVT and aspects of the invention are directed to that end.

SUMMARY OF THE INVENTION

In accordance with exemplary implementations of the invention, a method is provided for use by an implantable medical device capable of multi-site ventricular sensing within a patient. Intrinsic ventricular electrical events are detected by the device within the patient during a tachyarrhythmia at each of a plurality of different sites within the ventricles. Ventricular event timing differences are then detected between the ventricular events (as detected at the plurality of different sites.) The device compares the ventricular event timing differences during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient, such as event timing differences previously detected within the patient during sinus rhythm or extrapolated from sinus rhythm values. The device then distinguishes VT from SVT based on the comparison of ventricular event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences, at least in cases where the comparison is sufficient to allow such a determination to be made. In circumstances where the timing difference comparison is not sufficient to discriminate VT from SVT (such as if magnitude of any timing differences is below a noise level), morphological analysis can be additionally performed to distinguish VT from SVT. In this manner, timing differences between events sensed at different sites within the ventricles are employed—either alone in or combination with event morphology—to discriminate VT and SVT.

By exploiting ventricular event timing differences, VT can often be efficiently and reliably distinguished from SVT without the need to perform a more computationally intensive morphology comparison. Nevertheless, in circumstances where morphology comparison is needed, the device is equipped to perform such a comparison.

In various exemplary embodiments described herein, the implantable medical device is a pacer/ICD or a CRT-D equipped with separate RV and LV leads, each with tip and ring electrodes for bipolar sensing. During a tachyarrhythmia characterized by a high ventricular rate, the device separately detects ventricular depolarization events in the RV (i.e. RV QRS complexes) and in the LV (i.e. LV QRS complexes) and compares the relative timing of the events to detect timing differences between the RV and LV events (herein denoted T_(RV−LV).) Preferably, the timing differences are averaged over several ventricular beats to provide an average value for T_(RV−LV). For a given patient, T_(RV−LV) might be positive, negative or zero. The average value for T_(RV−LV) is compared against a predetermined supraventricular RV−LV timing difference (herein denoted T_(RV−LV/SV)), which may have been obtained in advance within the patient during normal sinus rhythm or extrapolated from sinus rhythm values to take changes in ventricular rate into account. The subscript “SV” is used to indicate that this timing delay is representative of a supraventricular rhythm, which can include sinus rhythm.

In a first illustrative embodiment, T_(RV−LV/SV) is predetermined based on sinus rhythm timing delays, without taking into account possible variations in the timing delays due to increasing ventricular rate. That is, T_(RV−LV/SV) represents the average intrinsic RV−LV timing delay during normal sinus rhythm within the patient. For a given patient, T_(RV−LV/SV) might be positive, negative or zero. The particular T_(RV−LV/SV) value for the patient may be ascertained, for example, by an external programmer during a follow-up session with a clinician following implant of the device into the patient wherein sinus rhythm values are averaged. If so, the average value is then programmed into the implantable device. In other examples, the implantable device itself detects or updates the values for T_(RV−LV/SV) based on cardiac signals sensed within the patient during sinus rhythm. In any case, during a tachyarrhythmia, the average value T_(RV−LV/SV) is retrieved by the implantable device from memory for comparison against the current value of T_(RV−LV). The magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV) is calculated using T_(DIFF)=|T_(RV−LV)−T_(RV−LV/SV)|. If T_(DIFF) is relatively large (as determined using a suitable threshold T_(DIFF) _(—) _(MAX)), then the implantable medical device promptly identifies the ongoing tachyarrhythmia as VT without the need for any further analysis. In one particular example, T_(DIFF) _(—) _(MAX) is set to two times the standard deviation of the sinus rhythm RV−LV timing delay

In this regard, if T_(DIFF) is relatively large, that indicates that the difference between tachyarrhythmia event timing delays and the previously-detected sinus rhythm event timing delays is likewise relatively large. Any significant difference between tachyarrhythmia timing and sinus rhythm timing indicates that the tachyarrhythmia has a different origin from that of sinus rhythm. Since sinus rhythm is known to be of supraventricular origin, the origin of the tachyarrhythmia is thereby deemed to be non-supraventricular in origin and so the tachyarrhythmia is identified as VT. For further specificity, the device can also examine the signs of T_(RV−LV) and T_(RV−LV/SV). If the signs of T_(RV−LV) and T_(RV−LV/SV) are found to differ from one another (e.g. T_(RV−LV) is positive but T_(RV−LV/SV) is negative), then the sign reversal further confirms that the origin of the tachyarrhythmia is ventricular in origin. Note that, in this first illustrative embodiment, if T_(DIFF) is not found to be greater than T_(DIFF) _(—) _(MAX), then the origin of the tachyarrhythmia is deemed to be inconclusive, since T_(DIFF) is not large enough to warrant a determination of a ventricular origin.

In a second illustrative embodiment, the implantable medical device considers the current ventricular rate in determining T_(DIFF). More specifically, values of T_(RV−LV/SV) are obtained in advance for the patient over a range of sinus rhythm heart rates, including relatively high sinus rhythm rates. The T_(RV−LV/SV) values may be stored in a histogram as a function of rate. Based on the sinus rhythm values stored in the histogram, the implantable device then extrapolates into the VT/SVT zone to estimate values for T_(RV−LV/SV) values at the high ventricular rates associated with VT/SVT. These values are referred to herein as T_(RV−LV/SV)(rate) values. Alternatively, the T_(RV−LV/SV)(rate) values may be ascertained by an external programmer during a follow-up session, then programmed into the implantable device. In any case, upon detection of a tachyarrhythmia within the patient, the implantable device retrieves the particular value of T_(RV−LV/SV)(rate) appropriate to the current ventricular rate. The average value for T_(RV−LV) obtained during the tachyarrhythmia is then compared against T_(RV−LV/SV)(rate). The magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV)(rate) is calculated using T_(DIFF)(rate)=|T_(RV−LV)−T_(RV−LV/SV)(rate)|.

If T_(DIFF)(rate) is relatively large (i.e. T_(DIFF)(rate)>T_(DIFF) _(—) _(MAX)(rate) where T_(DIFF) _(—) _(MAX)(rate) is a predetermined rate-dependent threshold), then the device promptly identifies the ongoing tachyarrhythmia as VT. For further specificity, the device can examine the signs of T_(RV−LV) and T_(RV−LV/SV)(rate). If the signs are found to differ from one another, then the sign reversal further confirms that the origin of the tachyarrhythmia is ventricular. Note that, if T_(DIFF)(rate) is not found to be greater than T_(DIFF) _(—) _(MAX)(rate), then the origin of the tachyarrhythmia is deemed inconclusive.

In a third illustrative embodiment, the implantable medical device also takes QRS waveform morphology into account to provide further specificity, particularly in circumstances where the event timing analysis is inconclusive. In this regard, templates representative of SVT morphology (QRS_(MORPH/SVT)) and VT morphology (QRS_(MORPH/SVT)) are obtained in advance for the patient. The templates may be derived, for example, based on intracardiac electrogram (IEGM) traces obtained within the patient during previous episodes of SVT or VT. Upon detection of a tachyarrhythmia within the patient characterized by a high ventricular rate, the device retrieves the morphology templates as well as the appropriate value of T_(RV−LV/SV)(rate) for current ventricular rate. The average value for T_(RV−LV) is again calculated and compared against T_(RV−LV/SV)(rate) to determine a value for T_(DIFF)(rate).

As in the preceding embodiment, if T_(DIFF)(rate) is relatively large (i.e. T_(DIFF)(rate)>T_(DIFF) _(—) _(MAX)(rate)), then the device identifies the ongoing tachyarrhythmia as VT based solely on the timing difference. However, if T_(DIFF)(rate) is not large (i.e. T_(DIFF)(rate) T_(DIFF) _(—) _(MAX)(rate)), then the device compares the waveforms obtained during the tachyarrhythmia (QRS_(MORPH)) with QRS_(MORPH/SVT) and/or QRS_(MORPH/SVT) to distinguish between VT and SVT. If the QRS_(MORPH) is consistent with QRS_(MORPH/SVT) but not QRS_(MORPH/VT), then the tachyarrhythmia is identified as SVT. If the QRS_(MORPH) is consistent with QRS_(MORPH/SVT) but not QRS_(MORPH/SVT), then the tachyarrhythmia is identified as VT.

For additional specificity, the device can also examine the signs of T_(RV−LV) and T_(RV−LV/SV)(rate), as already discussed. Still further, the device can examine signals received from additional sensing sites such as signals sensed via LV or RV shocking coils. Sensing leads placed on or near the His bundle are also particularly useful for differentiating VT and SVT. Sensing sites in the atria can also be useful. Event timing and/or QRS morphology analysis can be applied to the additional signals to further confirm the discrimination of VT from SVT. The use of additional sensing sites may be particularly useful in circumstances where T_(DIFF)(rate)≦T_(DIFF) _(—) _(MAX)(rate) to provide further specificity.

In any of the various embodiments, once the type of tachyarrhythmia is determined, suitable therapy is delivered, such as Atrial ATP in response to SVT or cardioversion therapy in response to VT, if warranted. Appropriate diagnostic data can be stored within the device for subsequent clinician review. In some cases, warning signals can be generated to alert the patient to seek medical attention.

Thus, in the various exemplary embodiments just summarized, multiple sensing sites are used to monitor the timing of intrinsic heart events. Events with different origination typically present a different time sequence landmark/trace at different sensing sites, which the implantable system exploits using the aforementioned techniques to determine/discriminate the origin of the events and thereby discriminate VT from SVT. In addition to VT/SVT discrimination, the method can be used to detect premature ventricular contractions (PVCs) that originate in the ventricles. Although bipolar sensing examples have been described wherein “near field” signals are sensed in the ventricles using bipolar leads, “far field” sensing may also provide useful information. Also, it should be understood that the techniques described herein do not require both RV and LV sensing leads. In other examples, an RV lead is exploited that permits sensing at multiple sites in the RV, such as by using an RV tip/ring electrode pair to sense at one site and an RV coil to sense at another.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further features, advantages and benefits of the invention will be apparent upon consideration of the present description taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates pertinent components of an implantable medical system having a pacemaker, ICD or CRT-D equipped to implement event timing-based VT/SVT discrimination, supplemented by waveform morphology discrimination, where appropriate;

FIG. 2 is a flow chart providing an overview of the event timing-based VT/SVT discrimination techniques used by the system of FIG. 1;

FIG. 3 is a simplified illustration of the device of FIG. 1 along with a set of exemplary leads implanted in the heart of the patient, particularly showing, in stylized form, the conduction of electrical signals to the ventricles from the sinus node during sinus rhythm;

FIG. 4 is another illustration of the device of FIG. 1 particularly showing the conduction of electrical signals within the ventricles during a VT that originates in the RV;

FIG. 5 is another illustration of the device of FIG. 1, particularly showing the conduction of electrical signals within the ventricles during a VT that originates in the LV;

FIG. 6 is a flowchart illustrating a first exemplary discrimination technique in accordance with the general technique of FIG. 2, which exploits event timing differences between the LV and RV;

FIG. 7 is a flowchart illustrating a second exemplary discrimination technique similar to that of FIG. 6, but which additionally exploits the ventricular rate in assessing event timing differences;

FIG. 8 is a flowchart illustrating a third exemplary discrimination technique similar to that of FIG. 7, but which additionally exploits morphology templates to provide further specificity;

FIG. 9 is another illustration of the device of FIG. 1, particularly identifying the various electrodes of the set of exemplary leads; and

FIG. 10 is a functional block diagram of the device of FIG. 9, wherein the device is a pacer/ICD, illustrating basic circuit elements that provide cardioversion, defibrillation and/or pacing stimulation in the four chambers of the heart and particularly illustrating components for equipped to perform the various LV/SVT discrimination techniques of FIGS. 2-8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description includes the best mode presently contemplated for practicing the invention. This description is not to be taken in a limiting sense but is made merely to describe general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims. In the description of the invention that follows, like numerals or reference designators will be used to refer to like parts or elements throughout.

Overview of Implantable Medical System

FIG. 1 illustrates an implantable medical system 8 having a pacer/ICD or CRT-D 10 equipped with an event timing-based VT/SVT discrimination system for distinguishing VT from SVT within the patient in which the system is implanted. In the following examples, a pacer/ICD is described. Other implantable cardiac rhythm management devices can instead be used, such as CRT-D devices. In these examples, discrimination is achieved based on timing differences (if any) between LV and RV QRS complexes, along with, in at least some cases, morphological analysis of LV and RV QRS waveforms. The LV and RV QRS complexes are sensed via a set of pacing leads 12 implanted in the patient. In the example of FIG. 1, two leads—LV and RV—are shown (in stylized form) for sensing LV and RV IEGMs signals. A more complete set of leads is illustrated in FIGS. 3-5 and FIG. 9, described below.

Upon detection of a tachyarrhythmia characterized by a high ventricular rate, the pacer/ICD analyzes LV and RV IEGM signals to detect any event timing differences between RV and LV QRS complexes so as to assess the origin of tachyarrhythmia and classify the tachyarrhythmia as VT or SVT. In some examples, morphology-base discrimination is also employed. This will be described in detail below. Once a determination has been made as to whether the patient is suffering from VT or SVT, pacer/ICD 10 then delivers appropriate therapy, such as Atrial ATP in response to SVT or cardioversion shocks in response to VT.

In some embodiments, information pertaining to the tachyarrhythmia is transmitted to an external system, such as bedside monitor 14, which generates diagnostic displays alerting family members or caregivers. The bedside monitor may be directly networked with a centralized computing system, such as the HouseCall™ system or the Merlin@home/Merlin.Net systems of St. Jude Medical, for immediately notifying a physician of the tachyarrhythmia

Warnings pertinent to the particular tachyarrhythmia may also be generated using the bedside monitor, a hand-held personal advisory module (PAM), not separately shown, or an internal warning device provided within the pacer/ICD. The internal warning device (which may be part of pacer/ICD) can be a vibrating device or a “tickle” voltage device that, in either case, provides perceptible stimulation to the patient to alert the patient. The bedside monitor or PAM can provide audible or visual alarm signals to alert the patient or caregiver, as well as any appropriate textual or graphic displays. In addition, diagnostic information pertaining to the tachyarrhythmia may be stored within the pacer/ICD for subsequent transmission to an external programmer (not shown in FIG. 1) for review by a clinician during a follow-up session between patient and clinician. The clinician then prescribes any appropriate therapies, such as medications. The clinician may also adjust the operation of the pacer/ICD to activate, deactivate or otherwise control any therapies automatically provided by the device.

Additionally, the pacer/ICD performs a wide variety of pacing and/or defibrillation functions, such as delivering routine pacing or generating and delivering shocks in response to VF. Also, in some examples, the device is equipped to deliver CRT. Briefly, CRT seeks to normalize asynchronous cardiac electrical activation and resultant asynchronous contractions associated with CHF by delivering synchronized pacing stimulus to both ventricles. The stimulus is synchronized so as to improve overall cardiac function. This may have the additional beneficial effect of reducing the susceptibility to life-threatening tachyarrhythmias.

Thus, FIG. 1 provides an overview of an implantable medical system that includes an event timing-based VT/SVT discrimination system. Note that the particular shape, size and locations of the implanted components shown in FIG. 1 are merely illustrative and may not necessarily correspond to actual implant locations. In particular, preferred implant locations for the leads are more precisely illustrated and described with reference to FIG. 9.

Overview of Event Timing-based VT/SVT Discrimination

FIG. 2 provides a broad overview of the discrimination technique performed by the pacer/ICD of FIG. 1. Initially, at step 100, the pacer/ICD detects intrinsic ventricular electrical events (i.e. QRS complexes) within the patient during a tachyarrhythmia at each of several of different sites within the ventricles, such as in the LV and the RV. At step 102, the device detects event timing differences (if any) between the events as detected at the plurality of different sites. This may be performed, for example, by comparing the timing of the peaks of corresponding QRS events as detected at the various sites. Any significant timing differences (especially relative to any timing differences that might otherwise occur during supraventricular rhythms such as sinus rhythm) are indicative of the origin of the tachyarrhythmia. This is shown by way of FIGS. 3-5.

FIG. 3 illustrates a normal sinus rhythm, which represents one type of supraventricular rhythm. Sinus rhythm originates at a sinus node 104 in the right atrium of the heart. Electrical signals are conducted via a normal atrioventricular conduction pathway 106 via an atrioventricular node (not shown) into the left and right ventricles. As can be seen, the conduction pathway eventually splits, with some of the signals triggering depolarization of RV myocardial tissue at a location 108 near the tip electrode of the RV lead. Other signals instead propagate into the LV, triggering depolarization of LV myocardial tissue at a location 110 near the tip electrode of the LV lead. (For clarity and simplicity, the various electrodes of the implanted leads are not individually identified by reference numerals in the figure. See, FIG. 9 and its descriptions below for further information regarding the location and functions of the various leads, electrodes and coils.)

Within a healthy heart, the myocardium of the LV and the RV depolarize concurrently during sinus rhythm such that there is no significant time delay between the RV and LV during normal sinus rhythm. For a particular patient, however, an intrinsic time delay between LV and RV depolarization might occur even during sinus rhythm (or during SVT) because of conduction defects or for other reasons. Typically, any intrinsic RV/LV depolarization delay occurring during sinus rhythm (or during an SVT) is fairly small, at least as compared to the RV/LV delays that can occur during VT. As will be explained below, the intrinsic RV/LV delay (if any) occurring within the patient during sinus rhythm can be detected by the pacer/ICD and exploited as part of the VT/SVT discrimination procedure.

FIG. 4 illustrates a VT with origin in the RV. The VT originates at a location 112 in the RV. Electrical signals associated with the VT are then conducted via an abnormal conduction pathway 114 from the RV to the LV. As can be seen, the conduction pathway first passes location 108 near the RV tip electrode where RV depolarization is detected. The conduction pathway continues into the LV where it passes location 110 near the LV tip electrode where LV depolarization is detected. As can be appreciated, there can be a significant delay between RV depolarization and LV depolarization during this type of VT, with the RV typically depolarizing in advance of the LV. This intrinsic RV/LV delay is typically much larger than the intrinsic RV/LV delay (if any) occurring during sinus rhythm (or during SVT.)

FIG. 5 illustrates a VT with origin in the LV. The VT originates at a location 120 in the LV (such as left ventricular epic.) Electrical signals associated with the VT are then conducted via an abnormal conduction pathway 122 from the LV to the RV. In contrast to the VT of FIG. 4, the conduction pathway of FIG. 5 first passes location 110 where LV depolarization is detected, then continues into the RV, passing location 108 where RV depolarization is detected. Again, there can be a significant delay between LV depolarization and RV depolarization during this type of VT, with the LV typically depolarizing in advance of the RV. This intrinsic RV/LV delay is again typically much larger than the intrinsic RV/LV delay (if any) occurring during sinus rhythm or during SVT.

Hence, as these figures illustrate, the magnitude of the intrinsic RV/LV depolarization delay within a patient can differ significantly between sinus rhythms and VT. This is exploited to distinguish VT from SVT (which, like sinus rhythm, is of supraventricular origin). Typically, the delay is greater during VT than SVT (the latter of which might not exhibit any significant delay, depending upon the heart of the particular patient.) Also, note that the sign of the RV to LV depolarization delay can become reversed during VT as compared to sinus rhythm, depending upon the point of origin of the VT. For example, in a patient where the RV depolarizes prior to the LV during sinus rhythm, the order might be reversed during a VT originating in the LV. As such, a sign reversal in the intrinsic RV/LV delay can be indicative of a VT (at least in cases where the RV/LV delay is of sufficient magnitude for any sign reversal to be meaningful.)

Returning to FIG. 2, at step 124, the pacer/ICD compares the event timing differences detected at step 102 with predetermined supraventricular event timing differences for the patient, such as event timing differences detected during sinus rhythm or extrapolated from sinus rhythm values (using techniques to be described below). In one example, the pacer/ICD retrieves a pre-stored supraventricular RV/LV time delay from memory that had been determined previously for the patient, perhaps during a post-implant follow up session between patient and clinician. That is, the device retrieves a supraventricular RV/LV delay value representative of the type of delay occurring during a supraventricular rhythm, such as the sinus rhythm illustrated in FIG. 3. As already noted, such delays (if present) are typically relatively small. Additionally, or alternatively, the device can retrieve information representative of the sign of the supraventricular RV/LV delay value for use in detecting any sign reversal.

At step 126, the pacer/ICD then distinguishes VT from SVT based on the comparison of the timing differences detected during the tachyarrhythmia and the predetermined supraventricular event timing differences for the patient (at least in circumstances where the event timing differences are sufficient to allow such a determination to be made.) Exemplary techniques will be described in detail below that examine both the magnitude and the sign of any timing differences. Additionally, as will be further explained, waveform morphology can be exploited to provide further discrimination specificity. In addition to VT/SVT discrimination, the pacer/ICD, at step 126, can detect PVCs that originate in the ventricles (i.e. the device can distinguish PVCs that originate in the ventricles from PVCs of supraventricular origin based on event timing differences.)

At step 128, appropriate therapy is then delivered, depending upon the capabilities of the device and device preprogramming. In response to VT, Ventricular ATP or cardioversion might be delivered. ATP is discussed in, e.g., in U.S. Pat. Nos. 6,907,286; 7,191,002; and 7,295,873. In response to SVT, atrial ATP or cardioversion might be performed (i.e. one or more shocks are delivered to the atria.) See, also, therapeutic techniques described in U.S. Pat. No. 7,245,967 that can be applied to supraventricular arrhythmias, depending upon the capabilities of the device. Note also that, if the ventricular rate exceeds a threshold indicative of VF, one or more defibrillation shocks will typically be delivered instead. (In such cases, the discrimination procedure of FIG. 1 need not be employed first. That is, upon detection of a ventricular rate indicative of VF, defibrillation shocks are promptly delivered, as VF is life threatening.)

Additionally, or alternatively, warning signals are generated (as mentioned above) and/or diagnostics data is recorded. The diagnostics can include data pertaining to the timing delays detected within the patient as well as the determination made by the device as to whether those delays are indicative of VT or SVT.

These are just some examples of operations that can be performed by the implantable device in response to the detection and discrimination of VT, SVT or other tachyarrhythmias. Other responses might be appropriate, as well, depending upon the needs of the patient and the capabilities of the implanted device.

VT/SVT Discrimination Examples

FIG. 6 illustrates a first exemplary implementation of the discrimination technique of FIG. 2 wherein sinus rhythm timing delays are exploited to determine supraventricular delay values without ventricular rate adjustment. Initially, at step 200, the pacer/ICD detects VT/SVT based on the current ventricular rate as determined, e.g., using a ventricular-IEGM signal. In one particular example, the rate is continuously detected and compared against a VT/SVT threshold (set, e.g., to 150 beats per minute (bpm)) and a higher VF threshold (set, e.g., to 200 bpm). If the rate exceeds the higher VF threshold, then VF is thereby detected and defibrillation shocks are delivered. If the rate only exceeds the lower VT threshold then VT/SVT is detected. Assuming VT/SVT is detected, then at steps 202 and 204, QRS events are separately detected in the RV and the LV. For example, if the implantable device is equipped with bipolar leads, then an RV QRS may be detected within an RV-IEGM sensed in a bipolar sensing mode using tip and ring RV electrodes. Likewise, an LV QRS may be detected within an LV-IEGM sensed in a bipolar sensing mode using tip and ring LV electrodes. (It should be understood that LV and RV QRS complexes are typically detected by the device during normal device operations. That is, the device does not detect these events only during SVT/VT.)

At step 206, the pacer/ICD detects timing differences (if any) between each RV QRS and its corresponding LV QRS and calculates an average difference (T_(RV−LV)). For example, the peak of the RV QRS may be designated as time t=0, with the delay then measured to the peak of the LV QRS. (Note that this Time Delay Will be Negative if the LV Depolarizes Before the RV.) At least several ventricular beats are examined to detect the delays such that the delay values can be averaged together to yield the value for T_(RV−LV). In some examples, a running average may be used.

At step 208, the pacer/ICD inputs an average timing difference (T_(RV−LV/SV)) between LV and RV QRS events that had been previously detected within the patient during sinus rhythm. Depending upon the particular implementation, the value for T_(RV−LV/SV) may be determined while the patient is in a sinus rhythm under clinician supervision during a follow-up session after device implant and then programmed into the pacer/ICD. In other implementations, however, the pacer/ICD periodically determines or updates T_(RV−LV/SV) whenever the patient is known to be in sinus rhythm, so as to automatically update the value.

At step 210, the pacer/ICD compares T_(RV−LV) against T_(RV−LV/SV) to determine a difference (T_(DIFF)) where: T_(DIFF)=|T_(RV−LV)−T_(RV−LV/SV)|. That is, T_(DIFF) represents the magnitude of the difference between the average RV−LV intrinsic depolarization delay during the current episode of VT/SVT and the average RV−LV intrinsic depolarization delay during sinus rhythm for the patient. The value of T_(DIFF) will be at or near zero if the episode of VT/SVT does not significantly change the intrinsic RV/LV delay for the patient (as is typically the case during SVT). Conversely, the value of T_(DIFF) can be relatively large if the episode of VT/SVT significantly changes the intrinsic RV/LV delay (as is typically the case during VT).

At step 212, the pacer/ICD then compares T_(DIFF) against a max threshold (T_(DIFF) _(—) _(MAX)) set, for example, to two times the standard deviation of T_(RV−LV/SV). In one particular example, a predetermined value for T_(DIFF) _(—) _(MAX) is input at step 208 along with T_(RV−LV/SV). In other examples, T_(DIFF) _(—) _(MAX) is calculated by the device based on input data. If T_(DIFF) exceeds this threshold (T_(DIFF)>T_(DIFF) _(—) _(MAX)), as determined at step 218, then the tachyarrhythmia is deemed to be VT. For further specificity, the pacer/ICD, at step 216, compares the signs of T_(RV−LV)−T_(RV−LV/SV) to determine if there has been a reversal in sign. That is, the pacer/ICD determines whether sign(T_(RV−LV)) is equal sign(T_(RV−LV/SV)). If the signs are not the same, then the tachyarrhythmia is VT (with the origin of the VT causing the sign reversal), as indicated at step 218. For example, the VT might cause the LV to depolarize prior the RV; whereas the opposite is true during sinus rhythm. The reasons for such a sign reversal were discussed above in connection with FIG. 5. If the signs are the same, then the tachyarrhythmia is also a VT, but one where the origin of the VT causes significantly different depolarization “arrival” times, as indicated at step 220. For example, the VT might arise from a point of origin in the ventricles such that depolarization of the LV is merely delayed relative to the RV (without a change in the order of depolarization.) Following either step 218 or step 220, VT therapy is delivered and warnings/diagnostics may be generated, as already discussed.

Note that, if at step 214, T_(DIFF) does not exceed the threshold (i.e. T_(DIFF)≦T_(DIFF) _(—) _(MAX)), then the source of the tachyarrhythmia is not yet determined (i.e. the discrimination is inconclusive), as indicated at step 222. (In this case, the difference between T_(RV−LV) and T_(RV−LV/SV) is not large enough to warrant VT/SVT discrimination. That is, “noise” in the T_(RV−LV) and T_(RV−LV/SV) data may exceed an acceptable amount required to reliably distinguish VT from SVT.) Processing returns to step 200 to detect and process additional data. In some cases, the additional data will enable the device to distinguish VT from SVT. If not, then additional or alternative discrimination procedures can be employed, depending upon the capabilities of the particular device, such as morphology-based techniques. These are discussed in further detail below. Note also that the two times standard deviation threshold for T_(RV) _(—) _(LV/SV) used at step 212 is merely exemplary. Otherwise routine experimentation may be performed in advance to determine alternative and/or optimal values for T_(DIFF) _(—) _(MAX). Such values can then be programmed into the pacer/ICD. To summarize, in one example, T_(DIFF) _(—) _(MAX) is determined as follows: measure time differences multiple times during sinus rhythm and then average the sinus time differences to yield T_(RV) _(—) _(LV/SV). T_(DIFF) _(—) _(MAX) can then be defined as two times the standard deviation of the sinus time difference measurements (T_(RV) _(—) _(LV/SV).)

Turning now to FIG. 7, an alternative implementation is illustrated that takes into account the current ventricular rate when assessing the difference between T_(RV−LV) and T_(RV−LV/SV). Many of the steps are the same or similar to those of FIG. 6 and so only pertinent differences will be described in detail. At step 300, the pacer/ICD detects VT/SVT based on the current ventricular rate and continues to track the ventricular rate during the arrhythmia. Assuming VT/SVT is detected, then at steps 302 and 304, QRS events are separately detected in the RV and the LV. At step 306, the pacer/ICD then detects timing differences between RV and LV QRS complexes and calculates an average difference (T_(RV−LV)).

At step 308, the pacer/ICD inputs an average supraventricular timing difference (T_(RV−LV/SV)(rate)) between LV and RV QRS events pre-determined for the patient for the current ventricular rate. This value may be extrapolated from sinus rhythm values. More specifically, rather than using a sinus rhythm RV−LV delay value (as in the preceding example) for use as the supraventricular RV−LV timing delay, the embodiment of FIG. 7 instead uses sinus rhythm delay values measured at different ventricular rates to estimate a corresponding RV−LV delay for the patient at VT/SVT rates. In one particular example, the pacer/ICD obtains and stores a histogram relating RV−LV intrinsic delays to ventricular rates for various sinus rhythm rates. For example, the histogram might specify a different value for T_(RV−LV/SV) for 60-80 bpm, 80-100 bpm, 100-120 bpm, 120-140 bpm, up to the VT/SVT threshold rate. Based on these values, the pacer/ICD (or an external programmer used to program the device) extrapolates to estimate values for rates in the VT/SVT zone, such as rates in the range of 140-160 bpm, 160-180 bpm, up to the VF threshold rate. Otherwise conventional numerical extrapolation techniques may be used to estimate these VT/SVT zone values from the lower sinus rhythm values.

Depending upon the particular implementation, the values for T_(RV−LV/SV)(rate) detected at sinus rhythm heart rates may be determined under clinician supervision during a follow-up session after device implant and then programmed into the pacer/ICD. For example, the patient may be directed to exercise so as to increase the rate throughout a range of rates from 60 to 140 bpm so as to obtain T_(RV−LV/SV)(rate) values for various sinus rhythm rates for storage in a histogram. The external programmer then analyzes the values of the histogram to extrapolate timing values at the higher rates in the VT/SVT zone. In some implementations, the pacer/ICD periodically determines or updates T_(RV−LV/SV)(rate) values at sinus rhythm rates whenever the patient is in sinus rhythm within a particular heart rate range. The device then performs the analysis to extrapolate the sinus rhythm timing delay values to yield estimated timing delays for use at the higher rates of the VT/SVT zone. Note that the number of bins in the histogram and the ranges of heart rates corresponding to each bin may be programmable values.

At step 310, the pacer/ICD compares T_(RV−LV) against the T_(RV−LV/SV) value for the current ventricular rate (i.e. T_(RV−LV/SV)(rate)) to determine a difference (T_(DIFF)(rate)) where: T_(DIFF)(rate)|T_(RV−LV)−T_(RV−LV/SV)(rate)|. That is, T_(DIFF)(rate) represents the magnitude of the difference between the average RV−LV intrinsic depolarization delay during the current episode of VT/SVT and the expected supraventricular RV−LV intrinsic depolarization delay determined for the patient at the current rate based on the aforementioned extrapolation. At step 312, the pacer/ICD then compares T_(DIFF)(rate) against a max threshold (T_(DIFF) _(—) _(MAX)(rate)) set, for example, to two times the standard deviation of T_(RV−LV/SV)(rate). This standard deviation is preferably derived from the standard deviation of multiple measurements of the supraventricular LV−RV time difference. As such, T_(RV−LV/SV) can be interpreted as the average of multiple measurements of the supraventricular LV−RV time difference and T_(DIFF) _(—) _(MAX)(rate) can be set to twice the standard deviation of these values. If T_(DIFF) _(—) _(MAX)(rate) exceeds the threshold, as determined at step 318, then the tachyarrhythmia is deemed to be VT.

For further specificity, the pacer/ICD, at step 316, compares the signs of T_(RV−LV)−T_(RV−LV/SV)(rate) to determine if there has been sign reversal. If the signs are not the same, then the tachyarrhythmia is VT with the origin of the VT causing the sign reversal, as indicated at step 318. If the signs are the same, then the tachyarrhythmia is also a VT, but one where the origin of the VT causes significantly different depolarization arrival times, as indicated at step 320. Following either step 318 or step 320, VT therapy is delivered and warnings/diagnostics may be generated, as already discussed.

If at step 314, T_(DIFF)(rate) does not exceed the threshold (i.e. T_(DIFF)(rate)≦T_(DIFF) _(—) _(MAX)(rate)), then the source of the tachyarrhythmia is not yet determined (i.e. the discrimination is inconclusive), as indicated at step 322, and processing returns to step 300 to detect additional data. As noted, in some cases, additional RV/LV timing data will enable the device to distinguish VT from SVT. If not, then additional or alternative discrimination procedures can be employed, depending upon the capabilities of the particular device, such as morphology-based techniques.

In FIG. 8, another alternative implementation is illustrated that takes into account the current ventricular rate when assessing the difference between T_(RV−LV) and T_(RV−LV/SV). In this embodiment, waveform morphology is also examined. Many of the steps are the same or similar to those of FIG. 7 and so only pertinent differences will be described in detail. At step 400, the pacer/ICD detects VT/SVT based on the current ventricular rate and tracks the ventricular rate. At steps 402 and 404, QRS events are separately detected in the RV and the LV. At step 406, the pacer/ICD detects timing differences between RV and LV QRS complexes and calculates the average difference (T_(RV−LV)). The pacer/ICD also records values representative of the shapes of the QRS waveforms (QRS_(MORPH)). That is, the device records the time-varying shape of the QRS or the device records some value or values representative of that shape, such as slop, half-height width, peak, width, zero-crossing points of the QRS complex, etc. Depending upon the implementation, QRS_(MORPH) may be based either on the LV QRS, the RV QRS or on some combination of the two.

At step 408, the pacer/ICD inputs T_(RV−LV/SV)(rate). As in the preceding example, this value may be extrapolated from sinus rhythm values. At step 408, the pacer/ICD also inputs VT and SVT QRS waveform templates (QRS_(MORPH/VT) and QRS_(MORPH/VT)) for the patient. QRS_(MORPH/VT) represents the typical shape of the QRS within the patient during VT. QRS_(MORPH/VT) represents the typical shape of the QRS within the patient during SVT. In one example, these waveform templates may be determined based on QRS waveforms detected within the patient during previous episodes of VT and SVT within the patient. For example, a clinician reviews recorded IEGM data for the patient to identify and distinguish prior episodes of VT and SVT within the patient. Based on this determination, an external programmer then generates QRS waveform templates for VT and SVT for programming into the pacer/ICD. Depending upon the implementation, QRS_(MORPH/VT) and QRS_(MORPH/VT) may be based either on the LV QRS, the RV QRS or on some combination of the two. The waveform templates may specify the time-varying shape of the QRS or may specify some value representative of that shape, such as the aforementioned values. In any case, during step 408, the pacer/ICD retrieves the previously-stored waveform templates from memory.

At step 410, the pacer/ICD compares T_(RV−LV) against the T_(RV−LV/SV)(rate)) to determine T_(DIFF)(rate). At step 412, the pacer/ICD then compares T_(DIFF)(rate) against T_(DIFF) _(—) _(MAX)(rate). If T_(DIFF) _(—) _(MAX)(rate) exceeds the threshold, as determined at step 418, then (as with the preceding example) the tachyarrhythmia is deemed to be VT. For further specificity, the pacer/ICD, at step 416, compares the signs of T_(RV−LV) to the sign of T_(RV−LV/SV)(rate) to identify any sign reversal. If the signs are not the same, then the tachyarrhythmia is VT with the origin of the VT causing the sign reversal, as indicated at step 418. If the signs are the same, then the tachyarrhythmia is also a VT, but one where the origin of the VT causes significantly different depolarization arrival times, as indicated at step 420.

If, at step 414, T_(DIFF)(rate) does not exceed the threshold T_(DIFF) _(—) _(MAX)(rate), then, at step 421, the pacer/ICD compares QRS_(MORPH) against one or both of QRS_(MORPH/SVT) and QRS_(MORPH/VT). If at step 422, QRS_(MORPH) is found to be consistent with QRS_(MORPH/SVT), then the arrhythmia is deemed to be VT, as indicated at step 424. If at step 426, QRS_(MORPH) is instead found to be consistent with QRS_(MORPH/SVT), then the arrhythmia is deemed to be SVT, as indicated at step 428. Otherwise conventional waveform comparison techniques may be employed to compare the various waveforms to determine if the waveforms are consistent with one another. In one example, the waveforms are considered to be consistent with one another is there is a substantial degree of similarity between the shape of the waveforms as assessed by some suitable numerical comparison parameter.

If QRS_(MORPH) is not found to be consistent with either QRS_(MORPH/VT) or QRS_(MORPH/SVT), the discrimination is deemed inconclusive, step 430. Although not shown in the figure, from step 430, processing can return to step 400 to detect additional data. Additional RV/LV timing data combined with additional morphological waveform data might enable the device to distinguish VT from SVT. If not, then additional or alternative discrimination procedures can be employed, depending upon the capabilities of the particular device, such as alternative morphology-based discrimination techniques. See, for example, the various patents cited above.

Following step 418, step 420, step 424 or step 428, suitable therapy is delivered based on the type of arrhythmia and/or warnings/diagnostics are generated, as already discussed.

What have been described are various exemplary techniques for discriminating VT and SVT using both RV and LV IEGM signals. To provide further specificity, additional IEGMs can be exploited, such as IEGMs sensed using one or more shocking coils. Sensing leads placed on or near the His bundle are also particularly useful for differentiating VT and SVT. Sensing sites in the atria can also be useful. Also, for multi-pole leads, various different electrode pair combinations can be exploited to sense additional IEGMs. Still further, it should be understood that the discrimination techniques do not require both LV and RV IEGMs. In some examples, particularly if a given LV lead or RV lead includes multiple electrodes for multi-site sensing, the discrimination techniques may exploit two or more IEGMs sensed in the same ventricular chamber, such as two or more LV IEGMs, or two or more RV IEGMs. In general, any combination near field or far field cardiac signals can be used so long as they provide a sufficient basis for distinguishing VT from SVT using the techniques described herein.

Note also that techniques have been described with respect to examples wherein the implantable system performs most or all of the operations. However, principles of the invention are applicable to other systems. For example, the discrimination technique may instead be performed by an external device (such as a bedside monitor) based on IEGM signals received from the implanted device. Exploitation of the invention within an implanted device is preferred as it allows the device itself to detect and discriminate tachyarrhythmias so as to deliver therapy promptly but implementations exploiting external devices can be useful as well.

For the sake of completeness, an exemplary pacer/ICD will now be described, which includes components for performing the functions and steps already described. As already noted, other implantable medical devices can instead be used, such as CRT-D devices. Note that, in a patient implanted with a CRT-D device, the RV lead is commonly used for pacing and sensing while the LV lead is mostly used for pacing only. However, intrinsic rhythms are presented at both leads, and state-of-the-art CRT-D systems are capable to collect sensing information from the left ventricle. The characteristics and the time sequence of the sensed event collections of the two leads are different for supraventricular- and ventricular-originated arrhythmia, as already discussed.

Exemplary Pacer/ICD

With reference to FIGS. 9 and 10, an exemplary pacer/ICD will now be described. FIG. 9 provides a simplified block diagram of the pacer/ICD, which is a dual-chamber stimulation device capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. To provide atrial chamber pacing stimulation and sensing, pacer/ICD 10 is shown in electrical communication with a heart 512 by way of a right atrial lead 520 having an atrial tip electrode 522 and an atrial ring electrode 523 implanted in the atrial appendage. Pacer/ICD 10 is also in electrical communication with the heart by way of a right ventricular lead 530 having, in this embodiment, a ventricular tip electrode 532, a right ventricular ring electrode 534, a right ventricular (RV) coil electrode 536, and a superior vena cava (SVC) coil electrode 538. Typically, the right ventricular lead 530 is transvenously inserted into the heart so as to place the RV coil electrode 536 in the right ventricular apex, and the SVC coil electrode 538 in the superior vena cava. Accordingly, the right ventricular lead is capable of receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle.

To sense left atrial and ventricular cardiac signals and to provide left chamber pacing therapy, pacer/ICD 10 is coupled to a LV/CS lead 524 designed for placement in the “CS region” via the CS os for positioning a distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. As used herein, the phrase “CS region” refers to the venous vasculature of the left ventricle, including any portion of the CS, great cardiac vein, left marginal vein, left posterior ventricular vein, middle cardiac vein, and/or small cardiac vein or any other cardiac vein accessible by the CS. Accordingly, an exemplary LV/CS lead 524 is designed to receive atrial and ventricular cardiac signals and to deliver left ventricular pacing therapy using at least a left ventricular tip electrode 526, a left ventricular ring electrode 525, left atrial pacing therapy using at least a left atrial ring electrode 527, and shocking therapy using at least a left atrial coil electrode 528. With this configuration, biventricular pacing can be performed. Although only three leads are shown in FIG. 5, it should also be understood that additional stimulation leads (with one or more pacing, sensing and/or shocking electrodes) might be used in order to efficiently and effectively provide pacing stimulation to the left side of the heart or atrial cardioversion and/or defibrillation.

A simplified block diagram of selected internal components of pacer/ICD 10 is shown in FIG. 10. While a particular pacer/ICD is shown, this is for illustration purposes only, and one of skill in the art could readily duplicate, eliminate or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) with cardioversion, defibrillation and pacing stimulation as well as providing for the aforementioned apnea detection and therapy.

The housing 540 for pacer/ICD 10, shown schematically in FIG. 10, is often referred to as the “can”, “case” or “case electrode” and may be programmably selected to act as the return electrode for all “unipolar” modes. The housing 540 may further be used as a return electrode alone or in combination with one or more of the coil electrodes, 528, 536 and 538, for shocking purposes. The housing 540 further includes a connector (not shown) having a plurality of terminals, 542, 543, 544, 545, 546, 548, 552, 554, 556 and 558 (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). As such, to achieve right atrial sensing and pacing, the connector includes at least a right atrial tip terminal (A_(R) TIP) 542 adapted for connection to the atrial tip electrode 522 and a right atrial ring (A_(R) RING) electrode 543 adapted for connection to right atrial ring electrode 523. To achieve left chamber sensing, pacing and shocking, the connector includes at least a left ventricular tip terminal (V_(L) TIP) 544, a left ventricular ring terminal (V_(L) RING) 545, a left atrial ring terminal (A_(L) RING) 546, and a left atrial shocking terminal (A_(L) COIL) 548, which are adapted for connection to the left ventricular ring electrode 526, the left atrial ring electrode 527, and the left atrial coil electrode 528, respectively. To support right chamber sensing, pacing and shocking, the connector further includes a right ventricular tip terminal (V_(R) TIP) 552, a right ventricular ring terminal (V_(R) RING) 554, a right ventricular shocking terminal (V_(R) COIL) 556, and an SVC shocking terminal (SVC COIL) 558, which are adapted for connection to the right ventricular tip electrode 532, right ventricular ring electrode 534, the V_(R) coil electrode 536, and the SVC coil electrode 538, respectively.

At the core of pacer/ICD 10 is a programmable microcontroller 560, which controls the various modes of stimulation therapy. As is well known in the art, the microcontroller 560 (also referred to herein as a control unit) typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, the microcontroller 560 includes the ability to process or monitor input signals (data) as controlled by a program code stored in a designated block of memory. The details of the design and operation of the microcontroller 560 are not critical to the invention. Rather, any suitable microcontroller 560 may be used that carries out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art.

As shown in FIG. 10, an atrial pulse generator 570 and a ventricular pulse generator 572 generate pacing stimulation pulses for delivery by the right atrial lead 520, the right ventricular lead 530, and/or the LV/CS lead 524 via an electrode configuration switch 574. It is understood that in order to provide stimulation therapy in each of the four chambers of the heart, the atrial and ventricular pulse generators, 570 and 572, may include dedicated, independent pulse generators, multiplexed pulse generators or shared pulse generators. The pulse generators, 570 and 572, are controlled by the microcontroller 560 via appropriate control signals, 576 and 578, respectively, to trigger or inhibit the stimulation pulses. The microcontroller 560 further includes timing control circuitry (not separately shown) used to control the timing of such stimulation pulses (e.g., pacing rate, atrioventricular (A-V) delay, atrial interconduction (inter-atrial or A-A) delay, or ventricular interconduction (V-V) delay, etc.) as well as to keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art. Switch 574 includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, the switch 574, in response to a control signal 580 from the microcontroller 560, determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, combipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art.

Atrial sensing circuits 582 and ventricular sensing circuits 584 may also be selectively coupled to the right atrial lead 520, LV/CS lead 524, and the right ventricular lead 530, through the switch 574 for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR. SENSE) sensing circuits, 582 and 584, may include dedicated sense amplifiers, multiplexed amplifiers or shared amplifiers. The switch 574 determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. Each sensing circuit, 582 and 584, preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control and/or automatic sensitivity control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The outputs of the atrial and ventricular sensing circuits, 582 and 584, are connected to the microcontroller 560 which, in turn, are able to trigger or inhibit the atrial and ventricular pulse generators, 570 and 572, respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart.

For arrhythmia detection, pacer/ICD 10 utilizes the atrial and ventricular sensing circuits, 582 and 584, to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. As used herein “sensing” is reserved for the noting of an electrical signal, and “detection” is the processing of these sensed signals and noting the presence of an arrhythmia. The timing intervals between sensed events (e.g., AS, VS, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves” or “Fib-waves”) are then classified by the microcontroller 560 by comparing them to a predefined rate zone limit (i.e., bradycardia, normal, atrial tachycardia, atrial fibrillation, low rate ventricular tachycardia, high rate ventricular tachycardia, and fibrillation rate zones) and various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy that is needed (e.g., bradycardia pacing, ATP, cardioversion shocks or defibrillation shocks).

Cardiac signals are also applied to the inputs of an analog-to-digital (A/D) data acquisition system 590. The data acquisition system 590 is configured to acquire intracardiac electrogram signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device 602. The data acquisition system 590 is coupled to the right atrial lead 520, the LV/CS lead 524, and the right ventricular lead 530 through the switch 574 to sample cardiac signals across any pair of desired electrodes. The microcontroller 560 is further coupled to a memory 594 by a suitable data/address bus 596, wherein the programmable operating parameters used by the microcontroller 560 are stored and modified, as required, in order to customize the operation of pacer/ICD 10 to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude or magnitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape and vector of each shocking pulse to be delivered to the patient's heart within each respective tier of therapy. Other pacing parameters include base rate, rest rate and circadian base rate.

Advantageously, the operating parameters of the implantable pacer/ICD 10 may be non-invasively programmed into the memory 594 through a telemetry circuit 600 in telemetric communication with the external device 602, such as a programmer, transtelephonic transceiver or a diagnostic system analyzer, or with a beside monitor 14. The telemetry circuit 600 is activated by the microcontroller by a control signal 606. The telemetry circuit 600 advantageously allows intracardiac electrograms and status information relating to the operation of pacer/ICD 10 (as contained in the microcontroller 560 or memory 594) to be sent to the external device 602 through an established communication link 604. Pacer/ICD 10 further includes an accelerometer or other physiologic sensor 608, commonly referred to as a “rate-responsive” sensor because it is typically used to adjust pacing stimulation rate according to the exercise state of the patient. However, the physiological sensor 608 may further be used to detect changes in cardiac output, changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states) and to detect arousal from sleep. Accordingly, the microcontroller 560 responds by adjusting the various pacing parameters (such as rate, A-V delay, V-V delay, etc.) at which the atrial and ventricular pulse generators, 570 and 572, generate stimulation pulses. While shown as being included within pacer/ICD 10, it is to be understood that the physiologic sensor 608 may also be external to pacer/ICD 10, yet still be implanted within or carried by the patient. A common type of rate responsive sensor is an activity sensor incorporating an accelerometer or a piezoelectric crystal, which is mounted within the housing 540 of pacer/ICD 10. Other types of physiologic sensors are also known, for example, sensors that sense the oxygen content of blood, respiration rate and/or minute ventilation, pH of blood, ventricular gradient, PPG etc. Multiple sensors may be provided.

The pacer/ICD additionally includes a battery 610, which provides operating power to all of the circuits shown in FIG. 10. The battery 610 may vary depending on the capabilities of pacer/ICD 10. If the system only provides low voltage therapy, a lithium iodine or lithium copper fluoride cell may be utilized. For pacer/ICD 10, which employs shocking therapy, the battery 610 must be capable of operating at low current drains for long periods, and then be capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse. The battery 610 must also have a predictable discharge characteristic so that elective replacement time can be detected. Accordingly, pacer/ICD 10 is preferably capable of high voltage therapy and appropriate batteries.

As further shown in FIG. 10, pacer/ICD 10 is shown as having an impedance measuring circuit 612 which is enabled by the microcontroller 560 via a control signal 614. Thoracic impedance may be detected for use in tracking thoracic respiratory oscillations; lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring respiration; and detecting the opening of heart valves, etc. The impedance measuring circuit 612 is advantageously coupled to the switch 574 so that any desired electrode may be used.

In the case where pacer/ICD 10 is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it detects the occurrence of an arrhythmia, and automatically applies an appropriate electrical shock therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller 560 further controls a shocking circuit 516 by way of a control signal 618. The shocking circuit 516 generates shocking pulses of low (up to 0.5 joules), moderate (0.5-10 joules) or high energy (11 to 40 joules), as controlled by the microcontroller 560. Such shocking pulses are applied to the heart of the patient through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode 528, the RV coil electrode 536, and/or the SVC coil electrode 538. The housing 540 may act as an active electrode in combination with the RV electrode 536, or as part of a split electrical vector using the SVC coil electrode 538 or the left atrial coil electrode 528 (i.e., using the RV electrode as a common electrode). Cardioversion shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with a VF event and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (i.e., corresponding to thresholds in the range of 5-40 joules), delivered asynchronously (since VF events may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller 560 is capable of controlling the synchronous or asynchronous delivery of the shocking pulses.

Insofar as tachyarrhythmia discrimination is concerned, the microcontroller includes a rate-based VT/SVT/VF detector 601 operative to detect a tachyarrhythmia affecting the ventricles based on the ventricular rate by, e.g., using one or more rate thresholds (such as a VT/SVT threshold and a higher VF threshold.) A VT/SVT discrimination system 603 is operative to distinguish VT from SVT in accordance with the techniques generally described above. The VT/SVT discrimination system includes an LV/RV event timing difference detector 605 operative to detect event timing differences between ventricular events as detected at a plurality of different sites within the ventricles via the RV and LV/CS leads. An LV/RV event timing difference comparison system 619 is operative to compare the ventricular event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient retrieved from memory 594. An event timing-based discrimination system 607 is operative to distinguish VT from SVT based on the comparison of the event timing differences made by LV/RV event timing difference comparison system 619, at least in circumstances where such a discrimination can be made.

Additionally, an LV/RV event morphology detection/comparison system 609 is operative to detect the morphology of the ventricular events and compare the morphology with VT and SVT morphology templates retrieved from memory 594. A waveform morphology-based discrimination system 611 is provided to further discriminate VT from SVT based on the waveform comparison made by morphology detection/comparison system 609.

A therapy controller 613 is operative to control delivery of therapy based on whether the ventricular arrhythmia is SVT or VT, such as by controlling the delivery of ATP. A warning/diagnostics controller 615 controls the generation of warning signals and diagnostic data based on the results of the operation of the other units of the microcontroller, such as the generation of warning signals for relaying to bedside monitor 14 to notify the patient and/or physician of the onset, duration and type of various tachyarrhythmias. Warning signals may be delivered to the patient via a warning device 617, which may be, e.g., a vibrational warning device or a device that provide a perceptible “tickle” voltage.

Depending upon the implementation, the various components of the microcontroller may be implemented as separate software modules or the modules may be combined to permit a single module to perform multiple functions. In addition, although shown as being components of the microcontroller, some or all of these components may be implemented separately from the microcontroller, as application specific integrated circuits (ASICs) or the like.

As noted, at least some of the discrimination steps or functions can be performed by an external device based on signals sent from the pacer/ICD. This is illustrated by way of VT/SVT discrimination system 621 of external programmer 602. Additionally or alternatively, the bedside monitor may also be equipped with such components.

In general, while the invention has been described with reference to particular embodiments, modifications can be made thereto without departing from the scope of the invention. Note also that the term “including” as used herein is intended to be inclusive, i.e. “including but not limited to.” 

1. A method for use by an implantable medical device capable of multi-site ventricular sensing within a patient, the method comprising: detecting intrinsic ventricular electrical events within the patient during a tachyarrhythmia at each of a plurality of different sites within the ventricles; detecting ventricular event timing differences between the ventricular events as detected at the plurality of different sites; comparing the ventricular event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient; and distinguishing a ventricular tachycardia (VT) from a supraventricular tachycardia (SVT) based on the comparison of the ventricular event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences.
 2. The method of claim 1 wherein the device is equipped with left ventricular (LV) and right ventricular (RV) leads and wherein detecting intrinsic ventricular electrical events during the tachyarrhythmia at each of a plurality of different sites within the ventricles includes separately detecting ventricular events within the RV and within the LV.
 3. The method of claim 2 wherein detecting ventricular timing differences LV includes detecting RV−LV timing differences (T_(RV−LV)) between the ventricular events as detected in the RV and in the LV.
 4. The method of claim 3 wherein comparing the ventricular timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences includes: comparing ventricular timing differences (T_(RV−LV)) detected during the tachyarrhythmia with predetermined supraventricular timing differences (T_(RV−LV/SV)) detected within the patient during a prior sinus rhythm.
 5. The method of claim 4 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if a magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV) exceeds a predetermined threshold.
 6. The method of claim 4 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if T_(RV−LV) and T_(RV−LV/SV) have a different sign.
 7. The method of claim 4 wherein average values for T_(RV−LV) and T_(RV−LV/SV) are employed in the comparison.
 8. The method of claim 3 further including detecting a current ventricular rate during the tachyarrhythmia.
 9. The method of claim 8 wherein comparing the ventricular timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences includes: comparing ventricular timing differences (T_(RV−LV)) detected during the tachyarrhythmia at the current ventricular rate with predetermined supraventricular timing differences (T_(RV−LV/SV)(rate)) determined for the patient for substantially the same ventricular rate.
 10. The method of claim 9 further including the prior steps of: detecting ventricular timing differences (T_(RV−LV/SV)(rate)) within the patient for a range of ventricular rates during sinus rhythm; and estimating ventricular timing differences (T_(RV−LV/SV)(rate)) for the patient for rates within a VT/SVT zone by extrapolating from the timing differences detected during sinus rhythm.
 11. The method of claim 9 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if a magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV)(rate) exceeds a predetermined threshold.
 12. The method of claim 9 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if T_(RV−LV) and T_(RV−LV/SV)(rate) have a different sign.
 13. The method of claim 9 wherein average values for T_(RV−LV) and T_(RV−LV/SV)(rate) are employed in the comparison for the current ventricular rate.
 14. The method of claim 3 further including: detecting ventricular event morphology (QRS_(MORPH)) during the tachyarrhythmia; and comparing ventricular event morphology (QRS_(MORPH)) detected during the tachyarrhythmia with predetermined ventricular event morphology templates.
 15. The method of claim 14 wherein comparing the ventricular timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences includes: comparing ventricular timing differences (T_(RV−LV)) detected during the tachyarrhythmia at the current ventricular rate with predetermined supraventricular timing differences (T_(RV−LV/SV)(rate)) determined for the patient for substantially the same ventricular rate.
 16. The method of claim 15 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if a magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV)(rate) exceeds a predetermined threshold and the detected ventricular events have a morphology consistent with VT.
 17. The method of claim 15 wherein distinguishing VT from SVT includes: identifying the tachyarrhythmia as VT if T_(RV−LV) and T_(RV−LV/SV)(rate) differ in sign and the detected ventricular events have a morphology consistent with VT.
 18. The method of claim 15 wherein distinguishing VT from SVT includes: identifying the arrhythmia as SVT if a magnitude of the difference between T_(RV−LV) and T_(RV−LV/SV)(rate) does not exceed a predetermined threshold and the detected ventricular events have a morphology consistent with SVT.
 19. The method of claim 1 further including detecting premature ventricular contractions (PVCs) that originate in the ventricles.
 20. The method of claim 1 wherein the tachyarrhythmia is initially detected based on a ventricular rate exceeding a rate threshold.
 21. The method of claim 1 further including delivering therapy in response to the tachyarrhythmia.
 22. A system for use by an implantable medical device capable of multi-site ventricular sensing within a patient, the system comprising: an intrinsic electrical event detection system operative to detect intrinsic ventricular electrical events during a tachyarrhythmia at each of a plurality of different sites within the ventricles; a ventricular event timing difference detection system operative to detect event timing differences between the ventricular events as detected at the plurality of different sites; a ventricular event timing comparison system operative to compare the event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient; and a tachyarrhythmia discrimination system operative to distinguish ventricular tachycardia (VT) from supraventricular tachycardia (SVT) within the patient based on the comparison of the ventricular event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences.
 23. A system for use by an implantable medical device capable of multi-site ventricular sensing within a patient, the system comprising: means for detecting intrinsic ventricular electrical events within the patient during a tachyarrhythmia at each of a plurality of different sites within the ventricles; means for detecting ventricular event timing differences between the events as detected at the plurality of different sites; means for comparing the ventricular event timing differences detected during the tachyarrhythmia with predetermined supraventricular event timing differences for the patient; and means for distinguishing a ventricular tachycardia (VT) from a supraventricular tachycardia (SVT) based on the comparison of the ventricular event timing differences detected during the tachyarrhythmia with the predetermined supraventricular event timing differences. 